The catecholamine neurotransmitter dopamine (DA) functions in neural circuits across phylogeny to modulate both simple and complex behaviors. In humans, DA signaling modulates arousal, cognition, reward, and motor function. Deficits in DA signaling are associated with multiple neuropsychiatric and neurodegenerative disorders including schizophrenia, attention-deficit hyperactivity disorder (ADHD), and Parkinson's disease. Temporal and spatial regulation of synaptic DA signaling is controlled by the presynaptic DA transporter (DAT). DAT localization and activity appear to be highly regulated, though the identity of, and roles played by, many DAT regulators in vivo is ill-defined. In the nematode Caenorhabditis elegans, synaptic spillover of DA produced by pharmacological or genetic loss of DAT (DAT-1) induces a locomotory phenotype called Swimming Induced Paralysis (SWIP). Thus, worms lacking DAT (dat-1) paralyze in a few minutes after swimming in a small volume of water whereas wild-type (N2) worms swim continuously. SWIP is induced by the release of vesicular stores of DA and can be suppressed by genetic elimination of the post-synaptic DA receptor DOP-3. To reveal genes necessary for regulating synaptic DA levels, we propose to carry out a forward genetic screen in the nematode, selecting for animals that exhibit reserpine-sensitive SWIP. Mutant lines will be grouped based on their complementation by N2, dat-1 and dop-3, and after sequencing of the DAT-1 gene. Following the identification of complementation groups, SNP mapping and whole genome sequencing will be employed to map the sites of mutations. RNAi phenocopy and transgenic rescue of SWIP will be used to functionally validate observed base-pair changes. To determine if these genes regulate DAT, swip lines will be subjected to behavioral analysis, including automated analysis of swimming, response to exogenous DA on solid surface, response to DAT inhibitors/substrates such as imipramine and amphetamine, and the presence of wild-type levels of DA uptake as assessed in primary cultures and in heterologous systems. Transgenic expression of GFP-DAT-1 will be used to evaluate the effect of mutations on DAT trafficking in vivo, and to demonstrate the specificity of these genes for DAT trafficking. For mutations that induce reserpine and DOP-3 dependent SWIP independent of DAT-1, we will assess the contribution of altered DA release through the controlled firing of DA neurons using Channelrhodopsin-2 selectively expressed in DA neurons. As C elegans express the canonical genes that dictate DA biosynthesis, packaging, metabolism and reuptake, our SWIP-based forward genetic screen may reveal genes that both support DA signaling in the nematode and that are conserved in vertebrates, including humans.